A known golf club has a head attached to an elongate shank. When the head is large, the club is known as a "wood", and when the head is plate-like, the club is known as an "iron". It is known to provide a golf club, particularly a "wood", with a curved striking face. This striking face is typically convex about a vertical axis, and convex about a horizontal axis. The horizontal and vertical axes are defined when the club is in the preferred orientation for striking a golf ball.
The curvature about a vertical axis is commonly called "bulge" and is used to reduce the effect of a poor swing by the golfer. The bulge thus reduces the tendency of a ball to hook or slice when the ball is struck with an open or closed club face because of the corrective spin placed on the ball when the face is open or closed.
The roll curvature provides increased compression of the golf ball to obtain greater driving distance.
In addition to roll and bulge, the face of the club may form an angle with the vertical. This angle is called "loft" and is the angle a plane tangent to the striking face forms with a vertical plane. The amount of loft determines the angle of the path of the golf ball with the horizontal.
U.S. Pat. No. 1,299,014 (O'Hara) discloses a golf club having bulge and roll with very large radii of curvature. This patent is primarily directed to the provision of an element which provides additional weight and is located on the back of the club.
U.S. Pat. No. 3,625,518 (Solheim) teaches a golf club wherein the sole of the club is curved upwardly from a central portion to both the heel and toe portions of the club. The club face has roll and bulge about orthogonal axes, wherein the bulge axis is parallel to the axis of the shank of the club.
U.S. Pat. No. 4,367,878 (Schmidt) discloses a golf club wherein the bulge is parabolic.